I wouldn't pay $500 for a grow book, maybe a cool antique book, but definitely not one on growing. Cannabis a herbaceous plant and responds to all the same techniques used in their cultivation. It's not some rare, exotic specimen. Sounds like they are taking (major) advantage of nieve new growers, disgusting imo.
Lp aero/nft hybrid rails (2)12 site systems, rooted clones(4wks old), under custom dual 600w cool tube hood, in a 4x4 area gets me 1-1.25#'s per system, or 2-2.5#s per 1200w. Large dwc tubs(23gal tote), scrogged gets me about the same, in the same area. I'm lazy and don't put too much effort in, if I did, I think 3lb in a 4x4 under 1000w is possible. My custom dual 600 hood gives good spread, but not great penetration, limiting my viable canopy height to around 24". I'm moving up to thouies soon, so with more light and better penetration, I see me getting close to 3lb/light, though I'm happy with 2-2.5#/light if it means less work.
In a professional grow house, with no height limitations and quality lighting and atmosphere, 3lbs per shouldn't be a problem.